Triggers and Rules

Creating a Trigger for an Action

This example shows how to create a Trigger that is compatible with the previous, more advanced “Hello world” Action example, which has multiple input parameters of different types, and connect them together using a Rule.

Manifest File

Example: “Hello world” Action with a compatible Trigger and Rule

package:
  name: hello_world_package
  version: 1.0
  license: Apache-2.0
  actions:
    hello_world_triggerrule:
      function: src/hello_plus.js
      runtime: nodejs
      inputs:
        name: string
        place: string
        children: integer
        height: float
      outputs:
        greeting: string
        details: string

  triggers:
    meetPerson:
      inputs:
        name: Sam
        place: the Shire
        children: 13
        height: 1.2

  rules:
    meetPersonRule:
      trigger: meetPerson
      action: hello_world_triggerrule

Deploying

$ wskdeploy -m docs/examples/manifest_hello_world_triggerrule.yaml

Invoking

First, let's try “invoking” the ‘hello_world_triggerrule’ Action directly without the Trigger.

$ wsk action invoke hello_world_package/hello_world_triggerrule --blocking

Result

"result": {
  "details": "You have 0 children and are 0 m. tall.",
  "greeting": "Hello,  from "
},

As you can see, the results verify that the default values (i.e., empty strings and zeros) for the input parameters on the ‘hello_world_triggerrule’ Action were used to compose the ‘greeting’ and ‘details’ output parameters. This result is expected since we did not bind any values or provide any defaults when we defined the ‘hello_world_triggerrule’ Action in the manifest file.

Triggering

Instead of invoking the Action, here try “firing” the ‘meetPerson’ Trigger:

$ wsk trigger fire meetPerson

Result

which results in an Activation ID:

ok: triggered /_/meetPerson with id a8e9246777a7499b85c4790280318404

The ‘meetPerson’ Trigger is associated with ‘hello_world_triggerrule’ Action the via the ‘meetPersonRule’ Rule. We can verify that firing the Trigger indeed cause the Rule to be activated which in turn causes the Action to be invoked:

$ wsk activation list

d03ee729428d4f31bd7f61d8d3ecc043 hello_world_triggerrule
3e10a54cb6914b37a8abcab53596dcc9 meetPersonRule
5ff4804336254bfba045ceaa1eeb4182 meetPerson

we can then use the ‘hello_world_triggerrule’ Action's Activation ID to see the result:

$ wsk activation get d03ee729428d4f31bd7f61d8d3ecc043

to view the actual results from the action:

"result": {
   "details": "You have 13 children and are 1.2 m. tall.",
   "greeting": "Hello, Sam from the Shire"
}

which verifies that the parameter bindings of the values (i.e, “Sam” (name), “the Shire” (place), ‘13’ (age) and ‘1.2’ (height)) on the Trigger were passed to the Action's corresponding input parameters correctly.

Discussion

Firing the ‘meetPerson’ Trigger correctly causes a series of non-blocking “activations” of the associated ‘meetPersonRule’ Rule and subsequently the ‘hello_world_triggerrule’ Action.
The Trigger's parameter bindings were correctly passed to the corresponding input parameters on the ‘hello_world_triggerrule’ Action.

Source code

Specification

For convenience, the Actions and Parameters grammar can be found here:

Triggers and Rules